Al-Qaeda-linked insurgent group Al-Shabab has claimed responsibility for a deadly attack Thursday at Mogadishu airport. At least 13 people were killed and scores were wounded when two explosives-filled vehicles blew up at the gates of Aden International airport, according to reports.

The spokesman for the African Union peacekeeping mission AMISOM could not be immediately contacted to establish if peacekeepers were among the dead.

Al-Shabab is in the third week of an offensive aimed at toppling the weak Western-backed government after years of bloody stalemate.

Al-Shabab, with support from foreign militants, has been stepping up its use of suicide attacks as a weapon.

The group claimed responsibility for Tuesday's assault on a Mogadishu hotel that killed 31 people, including many politicians.

Twin blasts in the Ugandan capital in July killed 76 people who had gathered to watch the World Cup final taking place in South Africa.

Prior to the Thursday's attack, the UN said more than 230 civilians had died in the latest clashes.

Ugandan soldiers make up the majority of the African Union (AU) peacekeeping forces protecting the Somali government.

The Ugandan government announced last month it would sent more troops to Somalia to bring the AU force up to its mandated strength of around 8,000.

The current insurgency, which has claimed more than 21,000 lives, flared up in 2007 following Ethiopia's invasion to topple the ruling Islamist regime.

Somalia has been without a stable government since strongman Mohamed Siad Barre was ousted in 1991.